The high pressure turbine nozzle of a gas turbine engine performs an aerodynamic function in that it accelerates and directs the hot gas flow from the combustor into the high pressure turbine rotor. As such, the turbine nozzle experiences large pressure loads across it due to the reduction in static pressure between inlet and exit planes. It also is exposed to high thermal gradients resulting from exposure to the hot gases of the engine flowpath and the cooling air used to prevent overheating of the turbine structures.
The support structure of the turbine nozzle reacts to the pressure loads at the inner and outer flowpath diameters. The loads are transferred out of the turbine structure through the cold structures into the engine casings and frame.
Turbine nozzles are typically constructed of nozzle segments having paired vanes. At the inner structural interface of the turbine nozzle, the nozzle segments are often attached to the inner support structure by a bolt or a combination of bolts and a clamping arrangement. The outer flowpath interface, which is normally combined with a turbine shroud support, uses no mechanical retention, but relies on the pressure load across the nozzle to maintain contact and seat the nozzle with the outer support structure. It is important, for reasons of good engine performance, that the inner and outer interfaces provide good air seals. The pressure drop across these interfaces is of similar magnitude to that across the turbine nozzle itself. Any air leaking across the interfaces will not have been accelerated to the turbine nozzle hot gas exit stream velocity and is therefore a chargeable performance loss to the turbine engine. Modern gas turbine engines make use of seals at these locations to allow relative axial motion of the inner and outer structures while maintaining air seals which provide minimal leakage across the inner and outer nozzle interfaces.
There are several problems in executing all of the above required features. Current designs produce relatively complex nozzle assemblies that require unacceptable amounts of time to assemble and disassemble. Installation and replacement of turbine nozzles substantially contributes to engine maintenance time requirements. Further, the air seal arrangements in such assemblies are often difficult to install and to inspect. In the competitive aircraft engine market it is important to ease the maintainability requirements for hot section structures such as turbine nozzle that need periodic inspection and replacement.
A need therefore exists for an improved mounting arrangement that provides for easy assembly and disassembly of the turbine nozzle in order to ease turbine engine maintenance.
Turbine nozzles are subject to very high temperatures that in modern engines can be in the range of 2000.degree. F. In order to extend the life of turbine hardware, cooling air is provided to such hardware in order to prevent its overheating from exposure to hot engine gases. Higher operating temperatures in today's most efficient engines require improved cooling to prevent overheating and damage to turbine hardware. As a result, a need exists for a turbine nozzle mounting arrangement that provides improved turbine nozzle cooling.